This application pertains to the art of spreaders for lifting containers and, more particularly, to such spreaders which are mountable upon the tines of a fork truck or the like.
It is common to removably mount spreaders on forks of lift trucks or the like for use in top lifting containers for transportation from one location to another, and for stacking or unstacking such containers. The spreader is quickly detachable from the fork tines so that the fork truck can be used for other conventional purposes.
When using a container lifting spreader with a fork truck or the like, it is often difficult for the vehicle operator to properly align the spreader frame with a container. It is also frequently difficult for the vehicle operator to properly align a container for stacking. This is because the vehicle has limited movement in certain directions, and such alignment is particularly difficult with a side loading-type of fork truck. In order to overcome these difficulties, many arrangements have been proposed for allowing shifting movement of the spreader frame itself relative to the fork tines in order that the spreader frame can be properly aligned with a container without requiring any movement of the vehicle. Prior patents disclosing arrangements of this type include Meister 3,176,866 and Levitt 3,387,730 who disclose arrangements wherein a special traversing mechanism is built into the vehicle between the fork tines and their mast in order to allow lateral movement of the forks relative to the mast and vehicle. However, there is no provision for power shifting the container lifting spreader frame rotatably or longitudinally of the fork tines in order to achieve alignment. Green 3,552,557 discloses an arrangement wherein the spreader frame is shiftable rotatably and horizontally in directions both parallel and perpendicular to the fork tines. In the Green arrangement, the base frame itself is shiftable rotatably relative to the fork tines and this requires extremely wide tine receiving beams on the spreader frame in order to provide sufficient clearance for the necessary rotational movement. The Green arrangement also requires modification of the fork tines by drilling holes therethrough for connecting hydraulic cylinders which move the frame rotatably and longitudinally of the tines. In the paragraphs beginning at lines 30, 40 and 47 of column 5, Green broadly suggests alternative arrangements which involve no more than speculation because it is not clear how the suggested alternatives would be arranged to operate. Rumell 3,688,933 discloses an arrangement wherein the spreader frame is movable in all directions relative to the fork tines but there is no power means for so moving the spreader frame. Kinross 3,709,392 is of interest for another arrangement similar to that disclosed by Green. Tredray 3,713,556 discloses a spreader frame mountable upon fork tines and having extensible side frame members for positioning the container engaging devices at the corners of different size rectangles for using the spreader with different size containers.